This study is designed to identify and compare the sensilla, associated with feeding on the tarsi and labella of both sexes of Tabanus nigrovittatus using scanning and transmission electron microscopy. In addition, behavioral and electrophysiological techniques will be used to determine the function of these sensilla. Experiments are designed to investigate the various factors involved in the initiation of probing, gorging, and cessation of a blood meal in females exposed in the laboratory to artificial feeding chambers. The effect of a blood meal on fecundity in autogenous females will be determined. A comparison will be made, using electrophysiological techniques, of the peripheral chemosensory input of autogenous versus anautogenous females to various chemicals, including blood, to determine if failure of autogenous females to feed in the field is due to peripheral or central processing.